Discoveries of animal embryos have profoundly improved our understanding of the early
evolution of animal development. However, the fossil record of early animal embryos is
extremely sparse. Here we present some three-dimensionally (3-D) phosphatized Archaeooides from the basal Cambrian in southern Shaanxi Province, China. The 3-D reconstructions
of a number of specimens, aided by high-resolution X-ray tomography, demonstrate that
these soft-bodied fossil organisms have a thick cyst characterized by pustule-like ornaments
and vesicular structures. Furthermore, a multicellular inner body undergoing palintomic
cell division is enclosed by the cyst. The suite of characters, including submillimeter to millimeter
scale, a palintomic pattern of cell division, and a complex cyst wall microstructure,
corroborate the hypothesis that Archaeooides fossils represent the embryonic remains of
animals. More specifically, the structure of the cyst wall bears close comparison to the resting
cysts of living invertebrates, allowing us to interpret Archaeooides as a diapause embryonic
stage adapted to the temporally and spatially heterogeneous redox conditions that extended
from the Ediacaran to the early Cambrian. The global distribution of Archaeooides indicates
that these conditions were geographically widespread. Ultimately, Archaeooides provides evidence
of the early evolution of this metazoan life history strategy as an adaptation to adverse
environmental conditions. Its widespread occurrence in both conventional and exceptional
taphonomic windows provides the potential for reconstructing its embryology and, by inference,
the developmental evolution of early animals and their body plans.